Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

G. S. Roonwal ¹, U. Vijaya Kumar ¹

Affiliations
1 Department of Geology, University of Delhi, Delhi 110007, IN

Abstract

Manganese nodules have been studied under the microscope with the use of reflected light and scanning electron microscope. Around the nucleus accretion of the diagenetically derived material is seen to take place giving rise to columnar or dendritic texture. Away from the nucleus textural variation and abrupt discontinuity in the nodule growth is observed indicating changes in depositional characteristics of ferromanganese oxides as the nodule grew. The intermingling of manganese oxides and silicate minerals, and sometimes iron oxides is common, generating discontinuities within the nodule texture. Scanning electron microscopic observations indicate that the material deposited on the surface is crystalline, non-crystalline, inorganic. organic or detrital in nature giving rise to different surface features such as botryoidal, consolidated compact layering or unconsolidated porous surface appearance.

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G. S. Roonwal ¹, U. Vijaya Kumar ¹

Affiliations
1 Department of Geology, University of Delhi, Delhi 110007, IN

Abstract

Sediment samples from NS Transect in the Central Pecific Ocean, comprising the Areas C. D. F and G investigated with the help of scanning electron microscopy reveal in-situ formation of several authigenic minerals within pelagic sediments, which affect their surface texture and morphology. Zeolite crystals developed in-situ are noted in the siliceous ooze in the north equatorial Pacific (Area C). Micronodules with well developed initial growth lines, formed authigenically are commonly observed in the siliceous debris-rich calcareous ooze of south equatorial Peciflc (Area F). Quartz and feldspars of detrital origin are also found in the sediment. Dissolution of biogenic debris is noted in them. However. undissolved radiolarian oozes are common particularly in the sediments from south Pacific. Authigenic phillipsite needles are identified in the sediments from Area G which falls within the Marquesas Fracture Zone.

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